1. Technical Field
The invention relates generally to pneumatic tools. More specifically, this invention relates to a pneumatic tool with a reverse valve having an overdrive for variable torque and speed.
2. Related Art
Heretofore, various types of reverse valves have been used in pneumatic tools, e.g., impact wrenches and pulse tools. For example, U.S. Pat. No. 5,083,619 to Giardino et al., and assigned to Chicago Pneumatic Tool Company, discloses a plunger type reverse valve for reversing the direction of a rotor in an impact wrench. U.S. Pat. No. 3,714,994 to Zoerner et al., and assigned to Gardner-Denver Company, discloses rotary reverse valves. Furthermore, the related art includes overdrive reverse mechanisms for hydraulic motors, see, e.g., U.S. Pat. No. 3,586,466 issued to Erickson. All the patents referred to herein are hereby incorporated by reference.
One of the disadvantages of pneumatic tools is the ability to obtain variable torque and variable speed in the same tool in both forward and reverse directions. This is important in applications such as large structure construction, demolition or repair, e.g., bridges. For example, one problem in these applications which has long existed and has not been adequately addressed is providing enhanced torque and speed for removal of a lug nut subject to corrosion, dirt, or paint. Typically, a worker has two impact wrenches available, a small light weight impact wrench and a large heavy impact wrench. The small impact wrench is used for the majority of the lug nuts so a worker does not get tired and for ease of manipulation. The large impact wrench is for removal of difficult lug nuts. Such a large impact wrench is heavy and cumbersome to carry when only needed for hard to remove lug nuts. Furthermore, carrying two impact wrenches to be available for the occasional hard to remove lug nut, is time consuming and inefficient.
Heretofore, variable torque and speed hydraulic motors have been disclosed. However, hydraulics when used on hand-held tools has several disadvantages. For example, hydraulics retains heat generated by friction, etc. Another disadvantage is that hydraulic fluid must be contained in a sealed system. If the hydraulic system does not have adequate seals, hydraulic fluid will be lost from the system resulting in slick fluid leaking on the tool.
Another disadvantage in a hydraulic system, such as disclosed in U.S. Pat. No. 3,586,466, is that as torque is increased, speed decreases. This is because pressurizing a single chamber between the rotor and housing with a noncompressible fluid causes the rotor to rotate at a first speed and torque. However, by pressurizing two chambers, the rotor rotates at an increased torque and decreased speed since hydraulic fluid is not compressible, and does not expand to fill an area. In contrast, when air is subject to an increased area, it quickly expands to fill that area. Accordingly, pressurizing two chambers with air results in an increased torque and increased speed. A useful analogy is a balloon filled with air exploding when poked with a pin. This is because air in the balloon is compressed and moves quickly to neutralize the surrounding air pressure. In contrast, a balloon filled with water when poked does not explode, but slowly leaks. This is because the water is not compressed.
While the related art provides for pneumatic tools having reverse valves, and hydraulic motors having variable speed and torque, none provide a pneumatic tool having a reverse valve with variable speed and torque, i.e., overdrive. Such a device is needed to solve the long-felt problems in the power tool industry which have not been heretofore adequately addressed.